The percentage of antibiotic precscriptions written for sinus infections cases in USA equalls about 20%.That’s an impressive statistic, given that doctors and public health officials have long doubted that antibiotics can successfully treat the condition.

A new study, published in the Journal of the American Medical Association, confirmed those doubts: The antibiotic amoxicillin was no better than placebo at improving the congestion, cough, runny nose, pain, and other symptoms that accompany sinus infections or acute sinusitis, researchers found.

“Compared to placebo, amoxicillin doesn’t seem to provide any benefits,” says lead author Jane Garbutt, an associate professor at the Washington University School of Medicine, in St. Louis. “In terms of patient satisfaction, side effects, symptom relief, days missed from work, et cetera, we did not see any difference.”

Most sinus infections are caused by viruses, which don’t respond to antibiotics. But even bacterial sinus infections rarely require antibiotic treatment, according to the Centers for Disease Control and Prevention. In most cases, both types of infection go away on their own in less than two weeks.

“Most patients get better despite antibiotics, not because of them,” says Garbutt. “There is a high rate of spontaneous resolution.”

Antibiotics would be more useful if doctors were able to distinguish between viral and bacterial sinusitis. But general practitioners have no tests at their disposal that reliably diagnose bacterial infections, Garbutt says, and in the study she and her colleagues were unable to identify any symptoms or other markers that predicted which patients would respond to antibiotics.

“The problem for primary care physicians is figuring out which patients would benefit,” she says.

The study included 166 people with moderate or severe sinus infections. Half of the participants took amoxicillin three times a day for 10 days, and the other half took a placebo on the same schedule. In addition, every patient was given acetaminophen, cough medicine, and decongestants to use as needed.

The two groups of patients improved at approximately the same rate. By day three, just over one-third of those in each group reported a lessening of their symptoms, a proprotion that increased to roughly 80% in each group by day 10.

The patients taking antibiotics did feel measurably better than the placebo group on day seven, but the researchers did not consider the difference to be clinically (as opposed to statistically) significant. On that day, the difference in the two groups’ quality of life—as measured by a scale appropriately named SNOT-16—was negligible, the study notes.